Godwin’s Law (a response to argumentum ad Nazium and reductio ad Hitlerum,[note 1] or a Hitler Card) was formulated by attorney Mike Godwin, former general counsel for the Wikimedia Foundation, in the 1990s, and states:

P2 - Person X wants to use birth control to solve the problem of overpopulation.

C1 – Therefore person X is like Hitler.

Or it could be an ad hominem attack such as saying “You are just like Hitler and therefore whatever you are arguing for is wrong,” without having any reasoning behind why this conclusion was reached.

Godwin’s Law does not dispute the validity or otherwise of references or comparison to Hitler or the Nazis. As such a comparison or reference may sometimes be appropriate in a discussion, Godwin has argued that overuse of the Nazi comparison should be avoided as it waters down the impact of any valid usage. In its purest sense, the rule has more to do with completely losing one's sense of proportion rather than just mentioning Nazis specifically.[3][4] The law was initiated as a counter-meme to flippant comparisons to the Nazis, rather than to invoke a complete ban on comparisons. As Mike Godwin himself wrote in 2008:[5]

“”When I saw the photographs from Abu Ghraib, for example, I understood instantly the connection between the humiliations inflicted there and the ones the Nazis imposed upon death camp inmates—but I am the one person in the world least able to draw attention to that valid comparison.

Additionally, Godwin made an appearance in Glenn Greenwald's Salon comments section in 2010 to confirm, as Greenwald put it in a column titled The odiousness of the distorted Godwin’s Law:

“”Godwin himself appears in comments (authenticity confirmed via email) to explain that his “law” sought to discourage frivolous, but not substantive, Nazi analogies and comparisons.[6]

Godwin said in 2017 that it's ok to call the alt-right Nazis, because many of them use Nazi symbols and express support for Nazi ideology.[7] He wrote in 2016:

“”To be clear: I don't personally believe all rational discourse has ended when Nazis or the Holocaust are invoked. ... But I’m pleased that people still use Godwin's Law to force one another to argue more thoughtfully.[7]

With the increase in the number of media for online discussion, Godwin's Law is now applied to any online discussion — be they mailing lists, message boards, forums, chat rooms, blog comment threads, or wiki talk pages.

Traditionally in many Internet discussion forums, it is the rule that once such a comparison is made, the discussion is effectively finished and whoever mentioned Hitler or the Nazis has automatically lost the debate, though it is considered sort-of acceptable if one immediately says "Pardon me for invoking Godwin's Law." The blogosphere has only heightened the prevalence of Godwin's Law, with Nazi references being dropped across the political spectrum, such as the liberal Daily Kos, right-wing religious strongholds such as Bill Donohue's Catholic League, and intelligent design advocates like the Discovery Institute.

Compared to other known blog-based laws, namely Poe's Law, Godwin's Law is quite well known in more mainstream areas.[8] Just to prove it, the law even has its own Wikipedia article.[9] In 2012 it was added to the Oxford Dictionary,[10] which means that in 500 years' time it will be reviewed by completely mystified college arts majors.

A number of corollaries have been proposed since the introduction of Godwin's Law.

In a hilarious instance of cosmic symmetry, a similar law applies to neo-Nazi boards such as Stormfront: as the discussion grows longer, the probability of someone calling their opponent a Jew approaches one. (For another version, replace Stormfront with Conservapedia and Jew with liberal.)

Another example of a corollary, and an early example, is called "Sircar's Corollary," which is: “If the Usenet discussion touches on homosexuality or Heinlein, Nazis or Hitler are mentioned within three days.”'[4]

Another corollary was proposed by "Buddy Larson" in the comments to a post by the libertarian Volokh Conspiracy blog (alleging that gun control caused Kristallnacht) in November 2010:

“”As an online discussion of an original post concerning Nazis or Hitler grows, the probability of observing a laboured and unwarranted retreat or appeal to Godwin's Law (of laboured, unwarranted retreat to Nazi or Hitler references) approaches one.[12]

The exact history of the law is debatable,[note 2] but it is claimed that Arken's Law has its roots in the days of HTML 1.0 and earlier (such as Usenet). Any accusations of Big Brotherism, utilizing newspeak, practicing doublethink, thought policing, sending updates down the memory hole or belonging to the Anti-Sex League would all be invocations of Arken's Law.

Researchers from the University College London attempted to formulate reductio ad Hitlerum into a Bayesian framework, presenting evidence that this is pretty much exactly how people processed the argument:[15]

Before Hitler was a thing, the typical point of comparison for worst person in the world appears to have been the Pharoah of the Biblical book of Exodus (his identity is uncertain, and he may be fictional, which makes it a weaker rhetorical comparison), although the likes of Judas Iscariot, Pontius Pilate, Napoleon Bonaparte, and (for Americans) King George III were occasional references.[16] They don't seem to have been used in an earlier version of Godwin's Law, possibly because the internet did not exist.

Some, such as author Robert J. Sawyer, have criticized Godwin's Law for implying the Holocaust was sui generis, a unique event that can never happen again. Consequently, he argues, people will be reluctant to issue comparisons for future situations until it is too late, and even if they try, Godwin's Law will be used to falsely shoot them down.[31]